The present invention relates to wireless alarm and security systems and in particular to a method and apparatus for initiating an alarm condition at a plurality of alarm devices upon sensing of an alarm condition at one or more alarm device.
Recent regulatory requirements oblige fire alarm system installers to install systems that indicate the presence of a fire at all detectors in the system upon sensing a fire at any one detector. For example, if a fire is detected in a kitchen, then the kitchen fire detector must sound and indicate an alarm condition, and all other fire detectors throughout the premises must be triggered to indicate the alarm condition.
This requirement is relatively easily complied with in wired alarm systems by wiring all detectors to each other such that if any one detector detects an alarm condition, it initiates an alarm condition in any or all of the remaining detectors. However, for detectors that are wireless and powered by batteries, the problem becomes more complex since each detector must inform additional detectors that an alarm condition has occurred. Typical receiver circuitry located in the additional alarm devices in order to detect transmissions in compliance with FCC regulations (Part 15) for low power security/fire transmitters require a significant amount of current to operate. Thus, it becomes very difficult to maintain reasonable battery life while complying with low power transmission regulations. According to FCC regulations the permissible power of the transmitted signal is so low that receiver sensitivity must be excellent in order to obtain satisfactory range, and such a level of receiver sensitivity reduces battery life to unacceptable levels.
Therefore, it would be advantageous if an alarm condition sensed by one sensor in a wireless alarm system would selectively trigger an alarm condition in any or all of the remaining detectors in the system. Furthermore, such a detector should be relatively low cost, efficient in terms of current consumption and should be sensitive enough to detect transmissions, which are compliant with the requirements of FCC regulations Part 15.
In an alarm situation, such as a fire, it is often useful to provide additional guidance beyond a multidirectional siren to those caught in the fire. In alarm systems of the prior art, various indicators of an emergency situation are activated at once with relatively little if any direction given to occupants on how to most effectively avoid danger.
Therefore, it would be advantageous to provide an alarm system capable of providing instruction and guidance regarding means of escape to those trapped in an emergency situation indicated by the alarm condition.
An additional requirement imposed on alarm systems is that of "temporal sounding". The sound made during an alarm condition in most commercial alarm system and many private alarm systems consists of a sequence of tones separated by an absence of these tones. The requirement of temporal sounding mandates that the sequence of tones emitted by any detector during an alarm condition be synchronized to those emitted by all other detectors active at the same time. Without the temporal sounding requirement such alarms would result in an essentially cacophonous mixture of alternately sounding detectors that potentially add to the confusion during an emergency situation. Conversely, if the tone emitted during the alarm condition were substantially continuous, then temporal sounding requirements would no longer be applicable since the difference in synchronization would only be detectable at the instant the alarm devices were first activated rather than continuously throughout their activation period. The specific tolerances governing synchronization are generally specified and enforced by the authority having jurisdiction (AHJ) in which the alarm system has been installed. As with the requirement of activating multiple detectors in response to an alarm condition, the requirement of temporal sounding is straightforward with wired alarm system but somewhat more difficult in wireless alarm systems since each alarm device operates independently from the remaining alarm devices.
Therefore, it would be advantageous if an alarm system would satisfy temporal sounding and multiple detector sounding requirements in addition to being wireless, low cost and efficient in terms of current consumption.